BIOLOGY 1A03 Lecture Notes - Lecture 23: Matthew Meselson, Franklin Stahl, Dna Replication
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BIOLOGY 1A03 Full Course Notes
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Dna replication and mitosis; module 2; theme 4; 19 oct 2014; textbook and module notes. Each strand in double helix acts as a template for replication. Other models included conservative and dispersive models. Two complementary parental strands somehow coming back together after replication. All four strands somehow combining into a mixture of old and new dna strand. Demonstrated replication by culturing e. coli in medium that contained nucleotide precursors with radioactively labeled heavy nitrogen isotope (15n) They transferred this bacteria into a 14n medium thus every new replicated strand would contain 14n isotopes. When bacteria from first medium centrifuged, only heavy 15n detected. When bacteria from second medium centrifuged, intermediate (b/w 14n-15n) detected indicating even distribution of 14n and 15n nucleotides in a double helix (conservative model fails here) When bacteria from third medium centrifuged, intermediate and light 14n detected, indicating semiconservative process is valid. Both require primer for initiation to occur and special proteins.